The present invention relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus suitably used for display of moving images.
Liquid crystal display apparatuses are used for personal computers, word processors, amusement equipment, TV sets and the like. Further study on liquid crystal display apparatuses is underway to improve their response characteristic for attainment of high-quality display of moving images.
Japanese Laid-Open Patent Publication No. 3-174186 (see FIGS. 1 to 4 of this publication) discloses a liquid crystal control circuit and a drive method for a liquid crystal panel that are adaptive to large-screen, high-resolution image display. Specifically, the publication discloses that the response time at rising of liquid crystal molecules can be shortened by comparing/operating the current voltage value being applied to the liquid crystal molecules and the voltage value to be applied in the next field with each other and correcting the voltage value based on the comparison/operation results.
The drive method for a liquid crystal panel disclosed in the above publication will be described with reference to FIG. 13. FIG. 13 shows a case that voltage data before correction changes from D1 to D5 in field F4.
As shown in FIG. 13, when voltages V1 and V5 are comparatively small, that is, close to a common voltage and the relationship of V5−V1>0 is satisfied, rising of liquid crystal molecules is slow, and thus it takes long time for the transmission amount to reach a predetermined value. Consider, for example, a reflection mode twisted nematic (TN) liquid crystal panel having a minimum voltage value of 2.0 V at which the liquid crystal layer permits no light transmission and a maximum voltage value of 3.5 V at which the liquid crystal layer permits transmission of the maximum amount of light. In this liquid crystal panel, when the applied voltage V1 is 2.0 V and the changed voltage V5 is 2.5 V, the time required for the transmission amount to reach the predetermined value is about 70 to 100 msec. Two or more fields are therefore required for the response, and this causes image smear.
As the voltage V5 is greater, the response time is shorter and will finally fall within 33 msec that is within two fields. Therefore, when the voltage V5 is less than a predetermined value, voltage data is corrected so that a voltage higher than V5 is applied in field F4 in which V5 is to be applied. To state specifically, the liquid crystal control circuit checks the voltage change amount for a given pixel by comparing data in field F3 with data in field F4, and controls a data corrector (see FIG. 2 of this publication) to correct the data in field F4 from D5 to D7, and a source drive IC (see FIG. 1 of this publication) to apply a voltage V7 to a source signal line based on the corrected voltage data D7 in field F4. In this way, the rising characteristic of the liquid crystal is improved, allowing attainment of a predetermined transmission amount T5 within one field shown by F4.
According to the liquid crystal panel described above, the response time can be improved to 20 to 30 msec by applying 3.0 to 3.5 V as the voltage V7.
In liquid crystal display apparatuses, high-speed response of liquid crystal is requested to present high-quality moving images without blurring. The response of liquid crystal can be sped up by the method disclosed in Japanese Laid-Open Patent Publication No. 3-174186 described above. However, under conditions of slow liquid crystal response, a difference arises between the transmittance of a liquid crystal panel in its steady state corresponding to the voltage value applied to the liquid crystal and the actual transmittance of the liquid crystal panel, and this causes a problem of failing in accurate correction of the voltage value. For example, in a low-temperature environment, in which the liquid crystal response speed is low, a target gray-scale level may not be attained even when it is about in the middle of the gray scale.
Moreover, in cases such as that the gray-scale level changes from a high level to a low level corresponding to a voltage value close to an extreme among the set gray-scale voltage values, and that the gray-scale level changes from a low level to a high level corresponding to a voltage value close to an extreme among the set gray-scale voltage values, the applied voltage to the liquid crystal panel is saturated, and thus a target gray-scale level may not be attained. In addition, if the voltage value correction method is low in precision, a practically usable corrected value may not be obtained, and thus a target gray-scale level may not be attained. If the next field is driven while a target gray-scale level has not been attained as described above, errors will be accumulated. As a result, image blurring may arise due to an afterimage in display of moving images, or a bright spot may be displayed at an end of a moving image.